1. Field of the Invention
The present invention relates to an image forming apparatus and, in particular, to an image forming apparatus having heads that eject liquid droplets.
2. Description of the Related Art
As an image forming apparatus such as a printer, a facsimile machine, a copier, a plotter, and a multi-task machine having plural such functions, a known image forming apparatus of a liquid ejection recording type uses a recording head that ejects, for example, ink liquid droplets. The image forming apparatus of this type ejects ink droplets onto a paper (not limited to a paper but including a member such as OHP to which ink droplets and other liquids can be attached; it is also referred to as a medium to be recorded on, a recording medium, a recording paper, a recording sheet, or the like) during conveyance from the recording head to perform image formation (used synonymously with recording, printing, and imaging). Examples of the image forming apparatus include serial-type image forming apparatuses in which a recording head ejects liquid droplets to form an image while moving in a main scanning direction and line-type image forming apparatuses using a line-type head in which a recording head ejects liquid droplets to form an image without moving.
Note that in the present invention, an “image forming apparatus” of a liquid ejection type refers to an apparatus that ejects ink onto a medium such as a paper, a thread, a fiber, a fabric, leather, metal, a plastic, glass, wood, and a ceramic so as to perform image formation. Further, “image formation” refers to forming not only relevant images such as characters and graphics but also irrelevant images such as patterns on a medium (i.e., only the ejection of liquid droplets onto a medium). Further, “ink” is not limited to one as generally called ink but is used as a generic name of various liquids available for image formation such as recording liquid, fixing treatment liquid, and liquid. Examples of the ink include DNA samples, resist, and pattern materials. Further, “images” are not limited to two-dimensional images but also refer to images added to three-dimensional objects and images obtained by shaping objects into three dimensions.
In such an image forming apparatus (hereinafter simply referred to as an “ink jet recording apparatus”), a recording head ejects ink from nozzles onto a paper to perform recording. Thus, due to an increase in the viscosity of the ink caused by the evaporation of a solvent from the nozzles, solidification of the ink, attachment of dust, mixture of air bubbles, or the like, the recording head is brought into an ejection failure state where recording failure is caused. Therefore, the image forming apparatus has a maintenance and restoration mechanism (maintenance unit) that maintains and restores the performance of the recording head.
For example, the maintenance and restoration mechanism has a cap unit (also referred to as a cap unit, a cap member, or the like) that seals the nozzles of the recording head. The cap unit is configured to cap the recording head when the image forming apparatus does not operate, thereby making it possible to prevent the ink inside the nozzles from drying and thickening. Further, in order to reduce the ejection failure of the ink, the maintenance and restoration mechanism is generally configured to appropriately perform a maintenance operation in which air bubbles, thickened ink, or the like are forcibly ejected from the nozzles of the recording head. The drainage of the ink thus ejected is ejected into the cap unit, and nozzle surfaces after being subjected to the maintenance operation are wiped and cleaned by a blade unit.
As a conventional image forming apparatus, Patent Document 1 discloses one having a head for ejecting black droplets and a head for ejecting color droplets and a maintenance and restoration unit that separately maintains and restores the heads.
Further, Patent Document 2 discloses one having head units in which plural ink heads are arranged in lines so as to be laid one on another and having cap units arranged at positions opposed to ink ejection surfaces and sealing nozzle lines. The head units are evenly arranged with spaces along their conveyance direction, and the cap units are retracted into their spaces at the time of ink ejection.
Moreover, Patent Document 3 discloses one having a maintenance unit including a holding member that holds sealing members in contact with the nozzle surfaces of a head. The holding member is capable of moving between a sealing position where the sealing members seal the nozzle surfaces and a retracted position where the sealing members are accommodated below a conveyance path, and is foldable between the sealing members. The holding member is extended upward at the sealing position and folded at the retracted position.
Furthermore, Patent Document 4 discloses one having one or more maintenance mechanisms that perform a maintenance operation on a head and a maintenance unit that retracts the one or more maintenance mechanisms so as to be vertically laid one on another above a position where a recording medium is conveyed at the time of ejection and on at least one of the supply side and the ejection side of the recording medium and then moves the maintenance mechanisms in a direction parallel to the conveyance direction of the recording medium.
Patent Document 1: JP-A-2009-202491
Patent Document 2: JP-A-2005-111939
Patent Document 3: JP-A-2008-229982
Patent Document 4: JP-A-2008-307714
However, in the conventional image forming apparatuses described above, the posture of the maintenance unit remains the same between a position opposed to the head and a position not opposed to the head. Therefore, the maintenance unit requires a large retracting space, which results in the size of the apparatuses being increased.
That is, in the image forming apparatuses having the plural recording heads that eject liquid droplets in, for example, a downward direction and the plural maintenance units having the cap units opposed to the plural recording heads from bottom sides thereof, when the maintenance units are horizontally moved to retracted positions, a retracting space corresponding to the widths of the maintenance units in a medium conveyance direction is required.